Sanding machine



Oct. 14, 1941. T. F. BRACKETT 2,258,733

SANDING MACHINE Filed Aug. 30, 1940 5 Sheets-Sheet 2 j' I l 2 l "Den OI.

, l?? Qmy mcfat Y l l i g attorneys Oct. 14, 1941. T. F. BRACKETT SA NDING MACHINE Filed A'ug. 30, 1940 Patented Oct. 14, 1941 tiene UNITED STATES PATENT 1 oEFicE i i i' General Motors Corporation, Detroit, Mich., a

corporation of Delaware Application August 30, 1940, Serial No. 354,865 8 Claims. (AC1. 51-t-189) This invention relates to the art of working surfaces in preparation for the applicationv of finish coatings as well as the smoothing and polishing of the applied coating. In the painting out of the path vof the leading roof surface of the oncoming body.

As a flexible backing for the abrasive, use is madevof an endless belt passing over a pair of of automobile bodies for example, the metal sur- SDaCed drums and Which e150 SerVeS by reason 0f face after being thoroughly cleaned is given a intermittent trai/e1 imparted t0 it, t0 renew the priming and one or more finish coats the latter abrasive 0r Polishing Surfaee- Tile renewal iSef' being preceded by proper sanding operations and feeted by employing an abrasive Strip haVmg 0pfoiioweoi by a iinal buiiing or polishing operation positepends secured t0 en unwinding rell con# involving the use of suitable abrasive material. 10 taining the Supply 0f UHU-*Sed vlStrip and When the smoothing operations are performed by t0 a Winding 1011 fOr taking UD dillled Strip With hand a great deal of time and effort is consumed, the Strip portion between the rolls embracing e with uniformity of result depending upon indirun of the belt and by reason of tension imposed vidual care exercised by the workmen. For bet- 0n bOth ends thereoreiinging friCtiOiially t0 the ter uniformity and improved working conditions belt so as to feed forwardwith belt travel. The the smoothing operations should be performed penodlc travel of thqbelt -15 m Short but' umform mechanically and the present invention relates Strokes asf predetermmed b5( the rate 0f Wea? of to apparatus for that purpose. n the abrasive and with tension on the rolls, the More particularly the apparatus is designed for abraslfe Str 1p 1?' fed forwarf at-the mt? of belt smoothing operations on metal roofs of automotravel u'respetwe Of'vanajtlons 1 n T911 dlameter' bile bodies which present surfaces of compound Cotn'nsatllrt frkihe mcelslg lglveterf curvature both longitudinally and transversely f n mg .roi Nif-a ug uh u1 et a rt- 'lvisthp and is for use in body manufacturing establishe Owadmum 01m en? .S' 0S m0 lon m e roll windingrmechaiiism is introduced through merfts employjmg comfeyor Systems by Whlch the 25- the use of a flexible motion transmitting con# bodies travel in following order at-a constant rate necton' Y O f Speed through success-ive Wolk performing Sta" For a more detailed explanation reference will 1510115 ACPrdmg-ly conveyor hue travel gures be made to the accompanying drawings wherein in the relative movement of the sanding head and Figure 1 is an elevation ofthe complete assembly the :Surface bemg Operate@ upon Wlth adqmonal viewed from the rear; 'Figure 2 is an enlarged relative movement occurring through reciproca-v View Viewed from the from; as Ori iirie 2 2 of tion of the sanding head and at a rate timed to Figure 4 and Showing ihe'sanding head mounted the speed of conveyor travel to insure proper ac- Ori the reciprocatory Carriage; Figure 3 is a ser? tion on the'entire surface. This Y enables the tional view ofthe sanding head taken on line presentation of a relatively small .area of abra-i 52 3 3 ef Figure 4; Figure 4 Shows the sending sive in the working zone to follow lbetter the irhead and crriage in Section as on une f i of regular curved roof surface. Conformity to Figure 1 and Figures 5 and 6 are detail sectional curvature is also insured by the use ofa flexible views teken respectively ou iiues 5 5 aud 5 5 endless belt acting as backing for the abrasive pad of Figure 2.A y y or facing and by mounting the sanding head for 40' While for the purpose of disclosure the invenvertical movementy on thejrecip'rocetine carriage tion is shown in its preferred embodiment as ap` and through a giinbal Oi universal jeint. u plied to roof surfaces of compound curvature it In COIlIleCtion With the mounting 0f the Sand will be understood that the mechanism will be ing head for vertical movement to follow the risel useful on flat or other types of surfaces and that and fall ofthe roof surface, provision is also made 4:5` the Vabrasive used may be of any VVtype ordinarily vfor retracting they head atthe end of the sanding employed forwet sanding, dry sanding or polish-` operation on one body for subsequent projection ing operations. For sanding operations,y the as the leading roof surface of the next body comes abrasive strip may consist of a length of Sandinto the working zone. The movement of the paper of the desired Vwidth having its opposite head away from` and towardV the work vsurface ends mounted on spools or 1drums so as to be fed may be controlled automatically and s-of espe# cial importance if the roof surface recedes from front to rear and through a wide'range, as it removes the head from the low position on-the from one to the other. While not shown in the drawingslthe Wet sanding will necessitate the use of suitable spray heads for delivering water in proper quantity to the surface being operated trailing surface of a body passing therebeyond upon.

As illustrated the work performing device is mounted overhead on a suitable framework above the conveyor line and is arranged to travel back and forth in a direction transverse to the longitudinal movement of the conveyor and additionally the head has a vertical movement transverse to both the direction of its reciprocation and the direction of conveyor travel to enable it to follow the rise and fall ofthe surface being operated upon.

In the drawings the reference numeral I indicates a conveyor truck or dolly supporting the body 2 and having a drag connection 3 with a continuously moving conveyor chain. Straddling the conveyor line is a framework consisting of one or more transverse beams 4 supported upon vertical posts 5-5. Suspended from the frame by dependent arms 6 is a transverse track or straight rail 1 on which is mounted a reciprocating carriage 8. To reduce friction the carriage is provided with a number of wheels or rollers to engage the several faces of the track bar 1 and motion is imparted to the carriage through a connecting rod or link 9 joined at one end to the carriage and at its opposite end to a rotating crank I0 forming a part of a gear reduction box II and being driven from an electric motor I2. For a conveyor line traveling at conventional speed the arrangement of the parts is such that carriage reciprocation is at a rate of about sixty strokes per minute.

Located within a guide opening in the carriage 8 and running against a number of antifriction rolls is a dependent bar or tube I3 which has the sanding head universally mounted in its lower end; The sanding head in the present instance includes a pair of spaced frame plates I4 and I5 fastened to a pair of spacers or tie straps I6, each having a central depression which cooperates with a removable cap I1 in providing a bearing for the transversely extending end pin I8 at each end of a cross piece or swivel block I9. Centrally of the cross piece I9 and through a bearing opening therein is l0- cated the longitudinal pivot pin for connection with the guide rod I3. By reason of the transverse pivot pins I8 and longituidnal pivot pin 2D the sanding head may rock in anydirection to conform to the surface being operated upon but in order to keep the head level when out of work engaging position a pair of tension springs 2|-2I on opposite sides of the joint extend between the head and the carriage in balanced relation.

Mounted between and in suitable bearings on the plates are a pair of transversely spaced rotating drums 22 and 23 to receive the endless belt or band 24 which provides a flexible or curve conforming backing for the abrasive strip and also serves by reason of its intermittent travel to fed the strip into the working zone. Along each edge of the belt and formed as an integral part thereof is an inwardly extending rib 25 arranged to ride within correspondingly formed annular grooves in the rolls 22 and 23 to prevent creep and give added strength to the belt edges. For maintaining the belt under proper tension a pair of idler rollers 26-26 engage the upper run of the belt and are carried in the pressure plate 21 fitted between the side plates I4 and I5 and held in proper adjustment by a series of four setscrews 28 threadedly engaged in suitable brackets 29 carried by the side plates. Also carried by the side plates are a pair of spaced rolls or spools 30 and 3| to which are secured the opposite ends of the sandpaper strip 32 having the portion between the rolls running under the belt and providing the work engaging facing.

The shaft 33 to which the spool 30 is keyed is rotatable in bearings in the side plates I4 and I5 and beyond the side plate I4 has iixed thereon an operating handle 34 and a brake drum 35. An external split clamping ring or brake band 3G embraces the peripheral surface of the drum 35 for frictional clutching engagement therewith. Its opposite ends terminate in a pair of laterally projecting ears or lugs 31 and 33 (see Figure 2) through which extends a headed stud 39 carrying a cooking lever 40 in the space between the lugsv 31 and 38 and an adjustable hand nut 4I against which is seated one end of a coil spring 42 surrounding the stud 33 and bearing at its opposite end against the lug 38 so as to exert an adjustable contracting force on the split braking ring 36. Secured at one end to the head of the stud 39 and anchored at its opposite end to an adjacent side plate I4 is a tensioning coil spring 43 which serves through the frictional engagement of the brake drum and braking ring to resist unwinding of the supply spool 30 and thereby take up slack in the sandpaper passing around the feed belt and maintain constant tension on the paper. The force of the spring 43 is overcome when a forward pull on the paper is exerted by travel of the belt so that the brake band 36 is moved with the roll until the cooking lever 40 by reason of its engagement with a fixed abutment 44 becomes tilted and exerts a spreading or prying force on the lugs 31 and 38 to expand the ring against the compression of the spring 42 and allow the brake drum 35 to slip relative thereto. At the end of the forward feeding stroke of the belt the pull of the spring 43 restores the position of the parts and tends to wind up the roll 30 to again maintain operating tension on the sandpaper strip 32,

The winding roll 3| adjacent the pay-olf end of the feed belt is keyed to a rotatable shaft 45 mounted in bearings in the sideframe members I4 `andlli with an operating handle 46 at one end together with a ratchet wheel 41 keyed thereto. A spring pressedpawl 48 is carried bythe frame to engage the teeth of the ratchet wheel 41 and prevent reverse rotation of the winding roll. The ratchet teeth are also engaged by a spring pressed pawl 49 carried by'Y rocking lever 5D fulcrumed on the shaft 45 to alord a one-way clutch action to wind up the roll upon swingingmovement'of the lever 50. y 1

The free end of the lever 5D is joined through a lost motion connection with oneend of a rock lever 5I fulcrumed on the mounting pin or axle of the belt roll 22. The lost motion connection may consist of a clevis 52 pivoted to the arm 50 and a clevis 53 pivotedto the arm 5I, each clevis head having a projecting pin fitted to a guide sleeve 54 and surrounded by a motion transmitting spring 55 seated at opposite ends on the clevis heads 52 and 53. Clockwise motion of the lever 50,l as seen iny Figure 2, will be transmitted through the coil spring 55 from the rock lever 5I While return motion of the parts will occur by reason of the interconnection of the sleeve 54 with the clevis pins. For this purpose at least one of the clevis pins should be slidable relative to the sleeve 54 within established limits and thereafter become locked for movement with the sleeve. Return movement of the lever 5| is :effected by the force of a wire spring 56 having one end bearing on the lever l and its other endV bearing on a xed stop on the framevand being located by an intermediate coilsurroundin'g .the

hub of a toothed ratchet wheelv 51 which isv keyed.

to the belt feed roll' 22. Forward motion" to the roll 22 is imparted through the ratchet wheel 51 by a pair of diametrically opposite spring pressed pawls 58-58 carried by the rock lever 5I.,

The opposite end of the lever '5I is formed with'v the head 59 arranged to be engaged rbythefendcf a piston plunger 60 contained within an air cylin-` indicated at 64 is hollow so as tozvent the air cylinfV der 6| whenthe valve is seated and is. arranged so that at one end of the limit of carriage stroke it' comes into engagementwith a bumper 65 tov unseat the valve. The bumper consists of a headed stud slidably mounted in an adjustable-attachment bracket 66 on the carriage rail` 1 in proper position as determined by the length of carriage stroke. To cushion impact-arubber nose I'61 is carried by the head. ofthe ystud 6 5 anda coil spring 68 is interposed between'the head and the mounting bracket so as' to yield slightly to vsliding movement of the headed stud 65 'when engaged forcibly by the valve plunger 64; I'

With each impulse given to the operating cylin-ider 60 as the carriage completes a reciprocating cycle, the lever 5I is rocked and through its one? way clutching engagement with the feed drum 22-` of sandpaper from the unwinding roll and si'mulf taneously, the windingdrum takes up a similar amount of dulled paper coming from the feed belt. The wind up of the roll 3l occurs by reason of the motion transmitted to it through the spring 55, the spring serving to maintain a tension on the paper at all times and to swing the lever 5U to a sufcient angle to take up all the paper fed forward regardless of the increasing diameter of the winding roll, all excess operating force being absorbed in compression of the spring so that there is a compensation for differences in roll diameter in relation to the fixed amount of paper fed forward. In any event the rate of feed is independent of roll diameter and is at the uniform rate of belt travel with the paper at all times being held under tension at both ends for a firm frictional engagement with the feeding belt.

It will be understood that the working pressure on the sandpaper amounts to the weight of the sanding head assembly and that any rise and fall of the curved work surface 'is followed by reason of gravity since the guide post I3 is free to slide vertically in the reciprocating carriage 8. Because the sanding head would tend to drop after the roof surface operated upon passes out of the sanding zone it is desirable that provision be made for retracting the sanding head in the interval between the travel of succeeding bodies out of and into the sanding zone. A suitable mechanism for this purpose, as illustrated in the drawings, includes the connection to the upper end of the guide bar I3 of an air cylinder 69 in which is fitted a stationary piston 16 connected by a rod 1l to a bracket or extension 8a on the reciprocating carriage 8. Air under pressure fed. to the upper end of. the cylinder WiIL'Ither'efore, tend, tofraise the 'sandmg head assembly upwardly out of the interference with the oncoming body and at the'proper time relief o fvpressu're will'allow the sand head to. be projected or dropped into engagement with the workgsurface. The supply of air under pressure isdeliv'ered through a. flexible hose 12 under control of a suitable valve 13.

As; .will be seenfin Figure 1 the operating connection'for thevalve Aincludesfa rock lever '14 holdingtthe valve in closed or cylinder bleed positionbyimeans of a coil spring-,15 and having a connection with `an electromagnet 16 which on energization'opensthe valve r13 to connect the fluid pressure source with the actuating cylinder. The; electrical circuit for the operating solenoid may becontrolledgby a conventionalV switch responsive to thefaction of la light sensitive or photocelliarrangement. :A s shown .in the drawing a light receivingjfdevice 11 and its cooperating light projecting device 18 are mounted on the vspaced supporting posts 5 so that the beam of light; is projected across: the path of bodies moving on thefconveyor'line. yIn this manner as'long asa bodytravels through the work performing Zonelthe Vprojection of the light beam to the Yreceiving y device 3 11 isl 'interrupted allowingl descent ofthe sanding head into work engaging relation while at times when `the beam is uninterrupted the sanding head is lifted to retractedposition. i

l Optionally thephotocell arrangement maybe employedalso for Vintermittent operation of the sanding; head reciprocating mechanism., It shouldg-,beymentioned that}while ,only a single sanding VAheadhas beenmeferred toas covering theentire'roof area and as completing thesandimg operation by' itself, an alternative arrangement;=contemplated includesjtwo or more heads operatingeither sideby side on the same track or in tandem on individual guide tracks.

The machine is universal in character in the sense that it can be used without modification or change on roofs of coupe, sedan and other types of bodies for any size chassis and regardless of variations in roof contours with changing design trends.

I claim:

l. In a device of the character described, a reciprocating sanding head including a pair of spaced drums, an endless belt embracing the drums, an abrasive strip in frictional engagement with one face of the belt, an unwinding roll for one end of the strip, a winding roll for the other end of the strip, a crank for rotating one of said drums to feed a given length of strip from the unwinding roll, and a flexible motion transmitting connection between the winding roll and said crank to rotate the roll for taking up slack in the forwardly fed Astrip and to introduce lost motion in compensation for variations in builtup roll diameter.

2. For sanding the curved roof of an automobile body as it travels forward on a conveyor line, a sanding head having a universal mounting, means accommodating head movement in a direction to and from the roof, other means to impart head movement across the roof and transversely of body travel, an abrasive facing strip carried by the head, an unwinding roll for the unused portion of the strip, a winding roll for the used portion of the strip, means associated with each roll to resist unwinding thereof and to maintain tension on the active portion, a supporting and feeding belt in frictional engagement with said active strip portion, and belt feeding and roll winding means operative periodically during head reciprocation.

3. In an arrangement of the character de scribed, a reciprocatory carriage, a sanding head movable therewith Yand including spaced apart winding and unwinding rolls, a strip of abrasive having opposite ends secured to the rolls and being arranged to pass from one to the other, a strip feeding and backing belt having frictional contact with the portion of the strip between said rolls to carry the same forward therewith, and intermittently operated means to rotate the belt and simultaneously the winding roll to take up the forwardly fed strip, said means rotating the belt and' roll differentially in automatic compensation for increasing winding roll diameter.

4. In an arrangement of the character described, a reciprocatory carriage, a sanding headY movable therewith and including spaced apart winding and unwinding rolls, an abrasive strip passing between the rolls, a feed belt affording a flexible backing shoe for the strip, spring means associated with onev roll to maintain tension on the strip, and spring means associated with the other roll to transmit winding motion thereto coincident with belt travel and to yield in com pensation for changes in roll diameter as affecting the rate of winding in relation to rate of belt travel.

5. In a reciprocating sanding head, means to feed an abrasive strip intermittently including an endless belt affording a iiexible backing shoe for the strip, a roll to wind up used strip :t'ed from the belt, a rock lever having aV one-way clutching action to transmit travel to the belt, a second lever having a one-way clutch connection with the winding roll, means operativeat aselective point in the range of head reciprocation to rock the first mentioned lever, and spring means; interconnecting said leversv for transmitting follow-up' motion to the. winding roll.w

6; In a sanding head of the 'character de-` means acting through the brake to resist chancey unwinding of the `r'ollV and means operative to release the brake atfa predetermined point in its travel. with `the unwinding roll' in opposition to the force of said. spring. means.

'7. In a sanding head of the character described, anfendless. band aiording a backing shoe for the abrasive. strip in the working zone of the head,V means to impartv periodic travel` to the band forI feeding strip into the working zone, a roll containing strip tofbe fed forward bythe band and means to maintain. the forwardly fed stripV under tension. including a brake frictionally engaging the. roll. and having a servo release responsive to pull: onthe strip as the band travels forward; and spring means acting on the brake and normally biasing the rolli in counterrelation to the direction of pull on the strip.

8. In. a sanding head yof the character described, an endless band affording a backing shoe for the abrasive stripA in the working zone of the head, means to impart periodic travel to the band for feeding strip intov the working z'one, spaced rolls for strip fed to and from the working zone, and meansl to maintain tension on the stripin the working `zone comprising? clutch mechanism associated with each roll and spring means acting through. said clutchmechanisms to bias both rolls intheir Trespective directions of winding.

TRACY F. BRACKETT.' 

